In deepwater offshore drilling operations using subsea BOPs, multiple wells may be drilled in series or in a batch mode. To illustrate, a subsea template may contain multiple wells. In some series drilling operations, a typical drilling process is to drill a complete well where a respective casing is set after drilling each section of the well. For example, after a first section of the well is drilled to a target depth, the section is set with a structural casing. A second section of the well is then drilled and set with a conductor casing. Another section of the well is then drilled and set with a surface casing. A high pressure wellhead is generally attached to the surface casing prior to running this casing string. A subsea blowout preventer (BOP) is then attached to the high pressure wellhead before proceeding with further drilling below the surface casing. After the subsea BOP is installed, one or more intermediate casings are then set in respective one or more sections of the well that are drilled in series below the surface casing. The production casing is then set in a respective section of the well that is drilled below the lowest of the one or more intermediate casings. Drilling of another well is then started where the drilling of the well and setting of the casings of the second well are performed in the same manner as in the first well.
In some other offshore drilling operations, some of the well sections of multiple wells are drilled and the respective casings are set in a batch operation. To illustrate, structural casings of multiple wells may be set after drilling respective sections of the multiple wells. Conductor casings of the multiple wells may then be set after drilling respective sections of the wells below the respective structural casings. The surface casings of the multiple wells may then be set after drilling respective sections of the wells below the respective conductor casings. Once the surface casings are set with its attached high pressure wellhead, further drilling below the respective surface casings requires installation of a subsea BOP on each well surface casing. However, due to the high cost of subsea BOPs, complexity of installing a subsea BOP, and the costs and risks associated with moving a subsea BOP from one well to another, further drilling below the surface casings of the wells are performed in series. To illustrate, sections of one of the multiple wells below the surface casing of one well are drilled and set with respective one or more intermediate casings and a production casing before drilling sections of another one of the wells below its surface casing. In general, after the intermediate and production casings of a first well are set, the subsea BOP that is attached to the surface casing of the first well is moved and attached to the surface casing of another well before drilling of the sections of the second well below the surface casing of the second well.
Because of differences in the drilling process, material, and equipment used in drilling of different sections of a well, drilling corresponding sections of two or more wells for intermediate and production casings before drilling further sections of the wells may result in reduction of drilling costs. Thus, a method and system of batch drilling that allows drilling and casing of corresponding sections of multiple wells may result in significant time and cost savings.